Feat add use custom dockerfile

[alekseybb197]

What does this change

Added command line flag to disable dockerfile generation. The flag changes the default behavior and causes the custom template to be used as is without changes.

What issue does it fix

Closes #2802

Checklist

• [+] Did you write tests?
• [+] Did you write documentation?
• Did you change porter.yaml or a storage document record? Update the corresponding schema file.
• If this is your first pull request, please add your name to the bottom of our Contributors list. Thank you for making Porter better! 🙇‍♀️

Reviewer Checklist

• Comment with /azp run test-porter-release if a magefile or build script was modified
• Comment with /azp run porter-integration if it's a non-trivial PR

[schristoff]

Due to discussions had in the Porter community meeting about this use case, we are deciding not to go forward with merging this feature into Porter. However, I'm happy to continue discussions on the issue to see if we can look into this again. :)

[alekseybb197]

I will keep my code for future discussions and work on it. Thanks!